ARCHIVED REPORTS_1989 - Laserfiche WebLink

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11 A minimum 18 -inch layer of vegetative cover soil placed over the low -permeability layer The vegetative soil cover will be fertilized, as necessary, and seeded with mod- erately rooted, erosion -resistant vegetation native to the surrounding area. Veg- etation that will germinate without irrigation and require minimum maintenance will be selected. Final cover slope and drainage details are shown on Drawing 4. Detailed construction guidelines for placement of final cover will be developed so that the final cover is completed consistent with the above requirements. 7.2 SETTLEMENT The settlement of refuse fill, characteristic of all landfills, is affected by a variety of factors, including (1) the types and moisture contents of refuse placed, (2) refuse density, (3) consolidation of the refuse under loads imposed by over- lying fill, (4) biological decomposition, and (5) chemical decomposition. The initial refuse density is estimated to be approximately 1,200 pounds per cu- bic yard. Further densification will occur from surcharge loading by successive lifts of refuse. Despite this densification process, refuse settlement after closure is estimated to range from 15 to 25 percent of the refuse thickness. This esti- mate is based on the method of preparation, effects of surcharging, estimated settlement during the active life of the landfill operation, refuse composition, and landfill settlement experienced at other sites with similar characteristics. The final surface grades are designed to accommodate drainage of the com- pleted landfill after settlement and to minimize erosion of the final cover. To ver- ify the integrity of the final cover, a program of periodic observation and mainte- nance will be instituted. Additionally, two permanent survey control monuments will be established and maintained to provide reference points for future settle - went measurements.